Farley Roger D
Department of Biology, University of California, Riverside, California 92521, USA.
J Morphol. 2005 Jul;265(1):1-27. doi: 10.1002/jmor.10227.
For the first time the scanning electron microscope was used to compare developmental changes in scorpion embryos and the first and second stadia. In the buthid species of this study, Centruroides vittatus, and all other scorpions, the newborn climb up on their mother's back and remain there without feeding for several days. At this location, they undergo their first molt and in a few days they disperse, fully capable of foraging in the terrestrial environment. The results here support earlier suggestions that the first stadium (pronymph) is a continuation and extension of embryological development. The first molt results in a nymph with exoskeletal features much like those in the adult. In the first molt the metasoma becomes relatively longer, and the sting (aculeus) becomes sharp and functional. The metasomal segments are modified for dorsal flexion and sting use. The embryos and the pronymphs have spiracles that open into an invagination near the posterior margin of flap-like abdominal plates in segments 4-7 of the ventral mesosoma. The second instars have spiracles that lead to book lungs farther anterior in sternites. Tubular legs with cylindrical segments in embryos and pronymphs become more sculptured and oval in the transverse plane. Each leg in the pronymph has a blunt, cup-shaped tip while distal claws (ungues, dactyl) are present in the second instar and subsequent stages. There are some sharp bristles and primordial sensilla in the pronymphs, but the second stadium has adult-like surface features: rows of knobs or granulations (carinae), serrations on the inner surfaces of cheliceral and pedipalpal claws, filtering hairs at the mouthparts, peg sensilla on the pectines, and mechano- and chemoreceptor sensilla on the body and appendages. Scorpion embryos and pronymphs have some structures like fossil scorpions thought to have been aquatic. There is a gradual development of features that appear to be terrestrial adaptations. Evidence is provided for the formation of the sternum from third and fourth leg coxal primordia and possibly from the first abdominal segment. This study is the first to provide evidence for a forward shift of the gonopore along with other structures in the anterior abdomen.
首次使用扫描电子显微镜比较蝎子胚胎以及第一和第二龄期的发育变化。在本研究的钳蝎科物种条纹正钳蝎以及所有其他蝎子中，新生蝎子会爬到母亲背上，在那里停留数天不进食。在这个位置，它们经历第一次蜕皮，几天后分散开来，完全能够在陆地环境中觅食。这里的结果支持了早期的观点，即第一龄期（幼体前期）是胚胎发育的延续和扩展。第一次蜕皮产生的若虫具有与成虫非常相似的外骨骼特征。在第一次蜕皮时，后体变得相对更长，毒刺（螫针）变得尖锐且具有功能。后体节经过改造以用于背部弯曲和使用毒刺。胚胎和幼体前期在中体腹面第4至7节的瓣状腹板后缘附近有开口通向内陷的气门。第二龄若虫的气门通向腹板前部更远位置的书肺。胚胎和幼体前期具有圆柱形节段的管状腿在横切面上变得更具纹理且呈椭圆形。幼体前期的每条腿都有一个钝的杯状末端，而在第二龄期及后续阶段则出现远端爪（爪、指节）。幼体前期有一些尖锐的刚毛和原始感觉器，但第二龄期具有类似成虫的体表特征：一排排瘤或颗粒（隆线）、螯肢和须肢爪内表面的锯齿、口器处的过滤毛、栉板上的栓状感觉器以及身体和附肢上的机械和化学感受器感觉器。蝎子胚胎和幼体前期具有一些类似于被认为是水生的化石蝎子的结构。逐渐出现了一些似乎是陆地适应性的特征。有证据表明胸骨由第三和第四腿基节原基以及可能由第一腹节形成。本研究首次提供了生殖孔与前腹部其他结构一起向前移位的证据。
